Rod to rod connector

ABSTRACT

A transverse connector having a seat rod for seating a rod therein engagement mechanism including a rod engagement seat forming a portion of the rod seat, the engagement mechanism being movable into and out of engagement with the rod seated in the rod seat.

This is a continuation application of U.S. Ser. No. 09/781,466, filedFeb. 12, 2001, now U.S. Pat. No. 6,602,253, which is incorporated hereinby reference.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention generally relates to orthopedic devices. Morespecifically, the present invention is a surgical tool or medicalconstruct used with spinal rods for the purpose of spinal fixation andcorrection of spinal curve.

2. Description of Related Art

Spinal rods are often used for spinal fixation, often times forcorrection of scoliotic curves. Fixation using such rods often involvesimplantation of rods and attaching them to the spine by hooks and/orscrews. Usually, a pair of rods are placed on opposite sides of theportion of the spine to be fixed.

Various systems have been developed for cross linking spinal rods toprevent rod migration and to increase stiffness of the paired rodassembly.

Many assemblies used for interconnecting spinal rods, commonly referredto as transverse connector assemblies or rod to rod couplers, utilize aplate mechanism having openings therethrough for adjustably retaininghook systems that are bolted in place in the plate. Examples of suchsystems are in the U.S. Pat. No. 5,334,203 to Wagner, issued Aug. 2,1994 and U.S. Pat. No. 5,522,816 to Dinello et al., issued Jun. 4, 1996.The U.S. Pat. No. 5,498,263 to Dinello et al., issued Mar. 12, 1996discloses a transverse connector system utilizing set screws tointerconnect vertebrae coupling members while also using plate membersas described above for interconnecting the coupling members. A squaredunit is formed having two sides defined by the plate members and twosides defined by the spaced rod members.

The U.S. Pat. No. 5,312,405 to Korotko et al., issued May 17, 1995discloses a coupler used for interconnecting spinal rods wherein thecoupler itself is a two piece unit. The neck portion of each unit isinterconnected by a screw mechanism which clamps a male portion within afemale portion of the system. The system also utilizes coupler insertsor yokes which engage a rod and are compressed about the rod whendisposed within a seat portion of each coupler and compressed by aninstrument which engages the bottom of the rod between the rod and thespine and the top of the coupler.

In further attempts to overcome these problems, various patents havedisclosed devices wherein the set screw directly contacts the rod.Examples of such patents include U.S. Pat. No. 6,113,600 to Drummond etal, U.S. Pat. No. 5,624,442 to Mellinger et al, and U.S. Pat. No.5,601,552 to Cotrel. In these patents, the force required to lock theset screw causes deformation of the rod at the point of contact of theset screw. This is more severe in cases where the set screw tip isconically shaped such as that found in FIG. 6 of the Drummond et alpatent. This causes deeper, more localized deformation and thereforestress inducing indentation that can cause lower rod fatigue life.Additionally, the depth of the notch, as well as the induced localizedstress is subject to random values based on how tight the surgeontightens the set screw at the time of surgery.

Numerous spinal rod systems have also been developed which providetransverse connectors for linking the adjacent spinal rods across thespinal midline to provide a rigid and stable construct. Most of thesesystems present one or more difficulties for spinal surgeons. Many ofthe devices are high profile which increases soft tissue trauma andsurgical complications. Furthermore, in many of these prior art systems,the attachment devices must be preloaded on the spinal rods which canrequire significant pre-operative planning and which virtuallyeliminates the opportunity to add connectors in situ.

One transverse connector system is the TSRH® CROSSLINK® of DanekMedical, Inc. The TSRH® CROSSLINK® utilizes a three point shear clampmechanism which restricts motion between the rods in all directions, andparticularly resists axial forces between rods and torsional momentsabout the axis of the rods. A quadrilateral construct is formed bylaterally connecting the rods across the sagittal plane with rigidplates. The lateral connection reduces the loss of correction that canoccur over time.

Rigid transverse connections between spinal rods are beneficial becausethey restrict rod migration and increase construct stiffness. In manycases involving multi-level fusion of the spine, these features areessential while solid bone fusion is accomplished. In the post-operativeperiod before fusion occurs, a significant amount of motion can occurbetween the rods, wires and hooks, which can, for example, allow ascoliotic correlation to decrease or the pelvis to de-rotate toward itsprevious, deformed position. By providing a rigid transverse connectionbetween two spinal rods, the loss of correction can be reduced and astiffer construct can be created which may enhance the promotion of asolid fusion. While the TSRH® CROSSLINK® provides an excellentconstruct, a need has remained for low profile devices where the surfacearea of contact with the rod is greatly increased and thus minimizeslocalized stress regardless of how tight the set screw is set.

It is desirable to provide a coupler which engages a rod by a simplelocking mechanism. It is also desirable to provide a simpleinterconnecting mechanism between couplers which requires few parts andlittle manipulation to provide the interconnection. Further, it isdesirable to provide a transverse coupler assembly which requires only asimple screw driver or nut driver outside of the assembly for itsinterconnection between a pair of spinal rods. It is also useful todevelop a mechanism having a surface area of contact with the rod thatis greatly increased and thus minimizes localized stress regardless ofhow tight the set screw is set.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a transverseconnector having a rod seat for seating a rod therein and an engagementmechanism including a rod engagement seat forming a portion of the rodseat, the engagement mechanism being movable into and out of engagementwith the rod seated in the rod seat.

DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention will be readily appreciated asthe same becomes better understood by reference to the followingdetailed description when considered in connection with the accompanyingdrawings wherein:

FIGS. 1A–C are side views, partially in cross section of a rod to rodcoupler made in accordance with the present invention,

FIG. 2 is a cross sectional side view of a rod to rod coupler made inaccordance with the present invention;

FIG. 3 is a side view, partially in cross section of a second embodimentof the rod to rod coupler made in accordance with the present invention;

FIG. 4 is a cross sectional side view of a rod to rod coupler made inaccordance with the present invention;

FIG. 5 is a side view, partially in cross section of another embodimentof the rod to rod coupler of the present invention;

FIG. 6 is a cross sectional side view of an embodiment of the rod to rodcoupler of the present invention; and

FIG. 7 is a side view of the set screw according to the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a transverse connector generallyindicated at 10 including a rod seat 12 for seating a rod 14 therein, anengagement mechanism 16 including a rod engagement seat forming aportion of the rod seat 12 wherein the engagement mechanism 16 ismovable into and out of engagement with the rod 14 seated in the rodseat 12.

By “engagement mechanism 44” as used herein, it is meant any item whichcan be used to hold a rod 14 in proper position within the rod seat 12.This engagement mechanism 44 can include, but is not limited to, alocking tab 16, and other similarly shaped devices which can providesufficient surface area contact with the rod 14. Critically, unlikeother point contact devices, the present invention provides a surface tosurface contact. Accordingly, deformation of the rod is minimized oreliminated.

In accordance with the present invention, a connector 10 is providedwhich includes an engagement mechanism 44 to rigidly hold spinalcomponents, such as two longitudinal rods 14, apart at variousdistances. A connector body 11, which is provided in multiple lengths inboth fixed and adjustable configurations, includes a seat portion 12 forsections of each rod 14. An engagement mechanism 44 is provided withinthe connector body 10 for each rod 14. The engagement mechanism 44includes a partial rod seat 12. A portion of the engagement mechanism44, sufficient to allow the connector body 11 to be pushed on the rod14, is free to move within the connector body 11. Thus the engagementmechanism 44 does not interfere with the placement of the connector body11 over the rods 14. When properly placed and sized, at least oneactuating mechanism 48 is tightened to secure the assembly 10. Thisforces the engagement mechanism 44 outward relative to the actuatingmechanism 48 and against the rods 14 while each of the rods 14 areforced against the seat portion 12 in the connector body 11.

The engagement mechanism 44 is held in place using an affixing mechanism20. This affixing mechanism 20 prevents undesired movement of theengagement mechanism 44. The affixing mechanism 20 can be a pivot, ascrew or other similar affixing devices known to those of skill in theart.

The single actuating mechanism 48′ embodiment is provided for simplelocking of close rod constructs. The actuating mechanism 48′ for thisembodiment consists of, but is not limited to, a set screw 18′ having aconical floating tip 32 or other tips known to those of skill in theart. This floating tip 32 compensates for manufacturing tolerances andprovides equal force against each engagement mechanism 44′ as the setscrew 18′ is advanced. This prevents localized stress, therebypreventing deformation of the rod 14′.

In one embodiment of the presents invention, there is provided anadjustable portion 34 which can consist of a male 38 and female 36portion. The male 38 portion includes a groove 42 and the said femaleportion 38 includes a set screw 18 with an angled or rounded tip. Theset screw 18, upon tightening, enters the groove 42 and securely holdsthe assembly 10 fixed at the desired length. The groove 42 providesincreased surface area for the set screw 18 to hold against.

More, specifically, the transverse connector 10 of the present inventionincludes an actuating mechanism 48 for moving the rod engagement seat 46into and out of engagement with rod 14 seated in the rod set 12. Theactuating mechanism 48 includes any mechanism wihich forcibly moves therod engagement seat 46 into and out of egagement with the rod 14 whilemaintaining the rod engagement seat 46 in the proper position. Thisactuating mechanism 48 can include, for example, multiple lockingpositions to keep the rod engagement seat 46 in a particular position.Alternatively, the engagement mechanism 46 can include a screw 18 whichcan be set to a specific tension based on the rod 14 being includedtherein and the specific tension required for the patient.

Additionally, the transverse connector 10 of the present invention caninclude a body portion 11 including at least one rod seat 12. Theengagement mechanism 44 includes an insert/locking tab 16 which ismovably connected to the body portion 11. In the preferred embodiment,the insert 16 is pivotally connected to the body portion 11 using anaffixing mechanism 20. For example, the insert/locking tab 16 can beconnected in any movable fashion known to those of skill in the art. Forexample, a screw, pivot pin, or other pivotable mechanism can beutilized.

The insert/locking tab 16 also includes a substantially arcuate recess22 located in the corner of the insert/locking tab 16. The recess 22defines the rod engagement seat 46 which is adjacent to the rod seat 12of the body portion 11.

Also included on the insert/locking tab 16 is an abutment portion 24.The abutment portion 24 is located on the surface of the insert 16 andis located opposite the arcuate recess 22. The actuating mechanism 48selectively engages the abutment portion 24 to selectively force thearcuate recess 22 towards the rod seat 22 thereby sandwiching the rod 14therebetween.

In the preferred embodiment, the actuating mechanism 48 includes a setscrew 18 threadedly engaged in the body portion 11. The set screw 18 isselectively movable towards and away from the engagement with theabutment portion 24.

An alternative embodiment of the present invention is shown in FIG. 1B.The insert/locking tab 16 is disposed in a recess 26 within the bodyportion 11. The insert/locking tab 16 Is slideable within the recess 26.

Also provided by the present invention is a transverse connector 10 asshown in FIGS. 5 and 6, including a pair of oppositely opposedinsert/locking tabs 16′. The inserts/locking tab 16′ are adjacent tospaced rod seats 12′ of the body portion 11′. Each of the abutmentportions 24′ of the inserts/locking tabs 16′ include a shoulder portion28 extending towards each other, as shown in FIGS. 5 and 6.

The actuating mechanism 18′ simultaneously engages each shoulder 28portion. The single actuating mechanism 48′ moves each of the inserts16′ into engagement with the rod 14′ and each of the rod seats 12′.

Additionally, the body portion 11′ of the transverse connector 10′ caninclude a threaded opening 30 whereby the shoulder portions 28 extendinto the opening 30 such that when the actuating mechanism 48′,including a set screw 18′, is threadedly engaged in the opening 30, theactuating mechanism 48 can simultaneously engage both shoulder portions28. This movement actuates movement of the inset/locking tab 16′ intoengagement with the rod 14′ seated in the rod seat 12′. Alternatively,the set screw 18′ can be placed into engagement using any lockingmechanism or manually being pushed into the opening 30.

In FIG. 1 the transverse connector 10 of the present invention alsoprovides a set screw 18′ which can include a floating tip 32 for evenlyapplying the load to both of the shoulder portions 28 simultaneously.The floating tip 32 self adjusts to evenly apply the load to bothinsert/locking tab 16′ simultaneously. This tip 32 prevents the setscrew 18′ from applying more pressure to one insert/locking tab 16′versus the other insert/locking tab 16′.

In a further embodiment, as shown in FIGS. 1 and 2, the transverseconnector 10 of the present invention provides a body portion 11 havingat least a pair of rod seats 12. In this embodiment, the body portion 11can include a length adjustment mechanism 34 for adjusting the distancebetween the pair of rod seats 12. In the preferred embodiment, the bodyportion 11 includes a first portion including one of the rod seats 12having a female opening 36 and a second portion including a second rodseat 12 and a male portion 38 which is slideably seated in the femaleopening 36. Also provided is a length locking mechanism 40 for lockingthe male portion 38 at a fixed position relative to the female portion36 thereby establishing a distance between the rod seats 12 and 12′. Thepractitioner, when inserting the mechanism, obtains precise distanceadjustments between rod seats 12.

The male portion 38 can also include a groove 42 along the length of themale portion 38. In this embodiment, the locking mechanism 40 includes aset screw 18′ for selective engagement with the groove 42.

Also provided by the present invention is a set screw which applies loadagainst an implant 51. The set screw 18′ can have a conical floating tip32 or other tips known to those of skill in the art.

The set screw 18′ distributes load between the two implant engagementmechanism 50, 52 in which the set screw 18′ is placed. The set screw 18′can therefore shift and distribute load between the two mechanisms 50,52 while securely locking an additional implant component in place.

In one embodiment of the present invention, the implant engagementmechanisms 50, 52 are both movable. Alternatively, one mechanism 50 canbe movable while the other mechanism 52 is fixed and therefore does notallow any movement.

Throughout this application, various publications, including UnitedStates patents, are referenced by author and year and patents by number.Full citations for the publications are listed below. The disclosures ofthese publications and patents in their entireties are herebyincorporated by reference into this application in order to more fullydescribe the state of the art to which this invention pertains.

The invention has been described in an illustrative manner, and it is tobe understood that the terminology which has been used is intended to bein the nature of words of description rather than of limitation.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. It is, therefore, to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described.

REFERENCES

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1. A transverse connector for engaging at least one rod comprising: arod seat for seating a rod therein; engagement means including a rodengagement seat forming a portion of said rod seat, said engagementmeans including an insert pivotally fixed to said connector capable ofrotating into and out of engagement with a rod seated in said rod seatand said insert including a substantially arcuate recess in one cornerthereof for engaging a portion of the rod and defining a second portionof said rod seat; and screw means for screwingly engaging said insertinto engagement with the rod seated in said rod seat.